My paper will assess from a philological point of view several claims about William of St. Thierry's use of patristic sources in a recent presentation of the cistercian monk's Exposition of Romans (S.R. Cartwright, Twelfth-Century Pauline Exegesis: William of St. Thierry's Monastic Rhetoric and Peter Abelard's Scholastic Logic, in: S.R. Cartwright (ed.), A Companion to St. Paul in the Middle Ages [Leiden-Boston 2013] pp. 205-234). Discussing several claims that contradict or simply neglect the results of my own previous research on the subject (G. Partoens, La présence d'Augustin dans l'"Expositio super epistolam ad Romanos" de Guillaume de Saint-Thierry, in: Sacris erudiri 44 (2005) pp. 285-300), I will try to show (1) to what extent William's commentary consists of quotations taken from the works of Augustine and Origen, (2) to what extent he borrowed his Augustinian quotations from the Pauline commentary by the Carolingian scholar Florus of Lyon, and (3) whether William's dependence on patristic quotations varies according to the Pauline chapters that are commented upon.